I'm not asking nor concerned about Fast Charge, I just want to know if I can SAFELY charge older iPhones (5/5S/5C/6/6S/SE/7) or older iPads (4/Air/Air 2/Mini/5/6) using the 30W USB-C Adapter (w/USB-C to Lightning Cable)? This would be for a situation where that would be the only charger I happen to have on hand. Thanks much for your time.

No cable is included. $49 gets you the adapter only. You will need a USB-C to USB-C or Thunderbolt 3 Cable to use this to charge your Macbook 12"

If you have a Macbook Pro 13" 2016 or newer you will need the 61W charger. If you have a Macbook Pro 15" 2016 or newer you will need the 87W version. In a pinch this would charge the larger Macbook Pros, but very slowly while not in use and is not officially recommended by Apple.

With all the new chargers apple has (5W, 10W, 12W, 30W, etc.) it isn't clear to me (or others) what the recommended chargers are to have. I see that there is a difference in USB as well (Type-A and Type-C) that can work with the phone too. When i've bought my older iPhones (3 to 7) they all came with the 5w USB Type A tiny charger and that didn't seem to give me the fastest time... While the specs of Watts, Volts, amps, are listed... its hard to just find a clear answer on time to charge because that is what we really care about.